18F-FDG micro-PET代谢显像评估大鼠放射性认知功能障碍的实验研究

Experimental study in the evaluation of radiation-induced cognitive dysfunction in rats via 18F-FDG micro-PET metabolic imaging

目的研究大鼠放射性脑损伤模型中葡萄糖代谢与神经元活性的相关性,探讨2-18F-2-脱氧-D-葡萄糖(18F-FDG)micro-PET用于放射性认知功能障碍评估的潜在价值。方法将3周龄雄性SD大鼠按照随机数表法分成对照组以及全脑照射组,每组10只,脑照射组利用小动物精确放疗仪给予10 Gy X射线照射,对照组不予照射。通过Morris水迷宫(MWM)实验评估大鼠认知功能,对两组大鼠脑部micro-PET图像数据进行对比分析,免疫组织化学染色检测神经元活性标记物c-Fos蛋白在脑内的表达变化,免疫荧光染色检测幼稚神经元标志物DCX及新生成熟神经元标志物BrdU/NeuN阳性细胞数的变化。结果照射3个月后,与对照组相比,全脑照射的大鼠在MWM定向航行实验中第2至4天的潜伏期均显著延长(t=2.179、3.393、3.219,P<0.05),MWM空间探索实验中的目标象限的探索时间百分比减少(t=3.857,P<0.01),提示全脑照射可引起海马依赖性认知能力下降;SPM分析micro-PET图像显示全脑照射组海马区域葡萄糖代谢显著降低(t=5.12,P<0.05);此外,全脑照射组海马区域神经元活性标记蛋白c-Fos的表达显著减少(t=14.22,P<0.01),幼稚神经元标志物DCX及新生成熟神经元标志物BrdU/NeuN阳性细胞数均较对照组减少(t=18.77、9.304,P<0.01)。结论全脑放疗后海马区域的葡萄糖代谢减低,与海马神经元活性下降及神经发生减少相一致,表明18F-FDG micro-PET可以作为评估放射性认知功能障碍的有效方法。

Objective To investigate the correlation between glucose metabolism and neuron activity in radiation-induced brain injury of rat,and to explore the potential implication of 18F-FDG micro-PET in the assessment of radiation-induced cognitive dysfunction.Methods Three-week-old male Sprague-Dawley(SD)rats were divided into two groups,whole-brain irradiation(WBI)group and non-irradiation control group,according to the random number table method.The WBI group was irradiated with 10 Gy X-rays using a small animal precise radiotherapy apparatus.Morris water maze(MWM)test was performed to evaluate the cognitive capability of rats.18F-FDG micro-PET covering the whole brain was conducted and the micro-PET images were processed by SPM software.The expression of neuronal activity marker c-Fos protein in rat brain was detected by immunohistochemical staining.The neuronal precursors marker DCX positive cells and newborn mature neurons marker BrdU/NeuN positive cells were detected by immunofluorescence staining.Results Three months after irradiation,MWM place navigation test showed that the latency of whole-brain irradiated rats was longer than that of the control group(t=2.179,3.393,3.219,P<0.05).In MWM spatial probe test,the percentage of target quadrant exploring time was reduced in the WBI group compared with the control group(t=3.857,P<0.01).These result suggested that WBI caused hippocampus injury-related cognitive decline.SPM analysis of micro-PET images showed that,after WBI,the glucose metabolism in the hippocampus was significantly reduced(t=5.12,P<0.05),the neuronal active marker c-Fos protein expression was significantly downregulated(t=14.22,P<0.01),and the neuronal precursors marker DCX positive cells and newborn mature neurons marker BrdU/NeuN positive cells were both decreased(t=18.77,9.304,P<0.01).Conclusions Glucose metabolism in the hippocampus was reduced after WBI,in consistent with the decrease of neuron activity and the reduction of neurogenesis in this area,suggesting that 18F-FDG micro-PET could be an effective method for assessing radiation-induced cognitive dysfunction.